Polysulfone resins are well known thermoplastic materials which, due to their many advantageous properties, find use as thermoplastic engineering materials. Because of their excellent mechanical properties polysulfone resins have been proposed for various utilities including those related to the medical field such as those relating to medical packaging, for example, containers in which syringes, surgical instruments, intravenous fluids, operating room devices, and the like are stored or maintained. Additionally, the polysulfones have been proposed for medical devices such as blood oxygenators, anesthesia canisters, blood leak detectors, blood centrifuge bowls, surgical instruments and operating room instruments. The toughness of the polysulfones as well as their optical clarity, high heat resistance, strength, and physiological inertness render them suitable for use in this area of medical devices and packaging. However, in order to be used in the medical field, as well as in some other areas, sterilization of these articles is often required.
A typical method of sterilizing various articles and objects useful in the medical field is through irradiation. The type of radiation usually employed is low level gamma or electron beam radiation. It is readily apparent that the level of such radiation which accomplishes the sterilization is significantly above that of ordinary background radiation. When exposed to radiation of sufficient intensity and duration to sterilize various objects made from polysulfone resins the resin material is subject to yellowing. This yellowing of the polysulfone changes the color of the resin, thus reducing its utility for this particular application. Not only packaging materials such as flexible polysulfone films and sheet products but also molded parts as well suffer from this yellowing phenomonon.
A new family of additives has been discovered which inhibits or reduces yellowing of polysulfone polymers after exposure to sterilizing irradiation. By sterilizing irradiation is meant irradiation which kills microorganisms.